Drilling platform

ABSTRACT

A floating platform for drilling after natural deposits beneath the floor of the sea. The platform has a reduced cross section at the sea surface, a service deck above the sea surface, and a substructure extending downwardly below the sea surface. The platform is monolithic and comprises a plurality of vertical cells of concrete. A bottom deck closes the bottom of the vertical cells and is adapted to be positioned deep below the sea surface and above the floor of the sea. The vertical cells are arranged such that at least one but not all of the cells extend from the bottom deck to the top deck and the center of gravity of the platform is below its center of buoyancy.

United States'Patent 11 1 1111" 3,824,943

M0 g 1451 July 23,1974

1 1 DRILLING PLATFORM 3,572,043 3 1971 Clara ..61 46 3,681,923 8/1972Hyde [76] Inventor- Gmnsundvelen 3,708,987 1 1973 Roulet (it al. 61 46Nesbru, Norway [22] Filed: Mar. 13, 1972 OTHER PUBLICATIONS The 011 andGas Journal of Sept. 14, 1970, pages 60,

[21] Appl. No.: 233,879 1 [30] Foreign Application Priority Data PrimaryExaminer-Jacob Shapiro Mar. 16, 1971 Norway 1008/71 Attorney AgentTaylor and Hinds [52] US. Cl. 114/.5 D, 114/.5 T, 61/465, ABSTRACT 175/7A floating platform for drilling after natural deposits beneath thefloor of the ea The platform has a re- Field of Search 61/465, T, ducedcross section at the sea surface, a service deck 114/5 D; 9/8; 175/7above the sea surface, and a substructure extending downwardly below thesea surface. The platform is [56] References Cited monolithic andcomprises a plurality of vertical cells UNITED STATES PATENTS ofconcrete. A bottom deck closes the bottom of the 2,940,266 6 1960 Smith61/465 vertical cells and is adapted to be Positioned p 55 4 below thesea surface and above the floor of the sea. 61/465 X The vertical cellsare arranged such that at least one 6 /465 but not all of the cellsextend from the bottom deck to 2,972,973 2 1961 Thearle 3,154,03910/1964 Knapp 3,273,526 9 1966 016m rh d g 11415 T the top deck and thecenter of gravity of the platform anning H4 .5 T v is below its centerof buo anc 3,510,892 5/1970 Monnereau et al 9/8 7 y y 3,535,884 10/1970Chaney 61/465 7 Claims, 2 Drawing Figures ,II'III' rIIII'II DRILLINGPLATFORM The invention relates to a floating drilling platform fordrilling after and production of natural deposits under the sea.

The new and characteristic which form the basis for the presentinvention, is the thought that a platform of that type which has areduced cross-section at the floating line, e.g. semi-submersible state,can be made monolithic of concrete as one or more vertical cells,preferably tube shaped, with a bottom. This very simple constructionwill, as showed below, offer many advantages compared with theconventional floating platforms.

For a better understanding of the invention it will be described furtherby means of an example.

FIG. 1 shows a vertical section B B through the platform and FIG. 2shows a horizontal section A A.

1 is a cell which is terminated under the water surface, 2 is a cellwhich is terminated above the water surface and 3 is a cell without abottom which the drill 4 passes through. 5 is the workingor service deckof the platform and 6 is the drilling tower.

The tubes may have varying wall thickness and diameter. It is, however,an advantage if the variations are small, since the platform in thatcase can be made by means of slip forms.

It will immediately appear from the figure that it is easy to achievethe center of gravity to be below the center of buoyancy and there arethus no problems at tached to the stability.

The cells may during the drilling be filled withair,

sand or water. There must always be some air present for buoyancy, whilesand is an excellent ballast material. Other solid ballast material, ofcourse, can be used. Water will be the natural medium for trimming.

The cells may also be used for tanks, e.g. for oil storage or as adumping place for polluted materials.

A series of advantages are achieved in that the drilling takes placethrough a tube. The work will not be hindered by waves or ice. Such asolution means a big advantage, especially for the divers, since theirwork often becomes restricted due to the difficulties in getting up anddown through the wave area. The tube will also beable to collect spillof oil, and prevent the oil from spreading in the sea.

As it appears from the figure, the platform will extend downwards muchdeeper than other floating platforms. The figure shows a platform whichhas a sub structure nearly double the height of the drilling tower,

e.g. a sub structure of 70 80 metres. This is 3 4 times the normal depthof a sub structure of a semisubmersible platform. At these depths thesea is practically calm irrespective of the waves on the surfaceThelarge weight of the concrete, the reduced cross-section of the platformat the floating line and possibly ballast of sand all adds to thestability, and the result is a platform whichv lies far more steady inthe sea than other floating platforms. In contrast to the existingplatforms, a platform according to the invention will thus not need tointerrupt the work due to bad weather. This is of large importance in socalled wild-cat"-drilling, and absolutely of vital improtance forproduction. None of the existing floating platforms may be used forproduction, namely because production must go on continouslyirrespective of the weather. The weight and stability of the platform isalso necessary, if it is to be provided with industrial plants,fishplate arrangements etc. The service deck can thus be provided withindustrial equipment, quay installations, and the like.

The large sub structure of the platform is also advantageous forconventional anchoring, since the anchors may be fastened far down andthus obtain a greater effect since the chain or the wire remains lyingmore horizontally. Dynamic anchoring may be employed.

The cell formed concrete structure is in itself particularly favourable.The construction can take up very large pressure-forces, since bucklingproblems practically do not exist. This is of importance with regard tothe large water pressures in question, and with more occasional localstresses, e.g. from ice.

A platform according to the invention offers no production difficulties,since the production can be performed exclusively by means of simplemethod and modest aids. A natural way is to cast the bottom and a bit ofthe walls in a dry-dock, tow this out to a deep sea area and thereaftererect the walls by means of slip forms, while the platform graduallysinks down in the water. Alternatively, the platform may be providedwith its own propulsion equipment.

Compared with a conventional semi-submersible platform, the platformaccording to the invention has the following advantages:

a. a simpler manufacture, b. a more robust construction,

c. substantially better stability,

d. no corrosion, i.e., little maintenance,

e. protection for the drilling work,

f. possibilities for collecting spill of oil,

g. cheap storage or oil etc.,

h. probably more favourable with regard to price and building time, i.conventional anchoring becomes more efficient. 'The platform is moredifficult to move than other floating platforms. This plays lessimportance if it operates within a limited geographical area, and iscompletely without inportance for a production platform.

It will immediately be understood that the design of the invention whichis shown on the drawing and described above, is only meant to illustratethe inventive thought, and that this may be varied in a series of wayswithin the idea of the invention.

1 claim:

1. In a floating platform for drilling after natural deposits beneaththe floor of the sea having a reduced cross section at the sea surface,a service deck above the sea surface and a sub structure extendingdownwardly below the sea surface, the improvement wherein said platformis monolithic and mobile, and comprises a plurality of contiguousvertical cells of concrete at least one of the cells lengthened to abovesea level to form a support for a service deck, a service deckpermanently fixed to said platform, the nonlengthened cells located asubstantial distance below the deck section so that the top of saidnon-lengthened cell or cells is at a substantial depth below the surfaceof the sea, a drilling structure on said service deck, a bottom deckclosing the bottom of said vertical cells and adapted to be positioneddeep below the sea sur- 7 face and above the floor of the sea, the wholestructure being constructed and arranged such that the center of gravityof said platform is below the center of buoyancy thereof.

2. An improved platform according to claim 1 further including a drillextending from said service deck down through one of said verticle cellsto the sea floor.

3. An improved platform according to claim 1 wherein said sub structureextends at least 70 meters below the surface of the sea.

4. An improved platform according to claim 1 wherein said platformincludes a first group of adjacent vertical concrete cells extendingfrom said service deck to said bottom deck and a second group ofvertical concrete cells in surrounding adjacency with said first groupand extending from said bottom deck upwards to ballast material.

1. In a floating platform for drilling after natural deposits beneaththe floor of the sea having a reduced cross section at the sea surface,a service deck above the sea surface and a sub structure extendingdownwardly below the sea surface, the improvement wherein said platformis monolithic and mobile, and comprises a plurality of contiguousvertical cells of concrete at least one of the cells lengthened to abovesea level to form a support for a service deck, a service deckpermanently fixed to said platform, the non-lengthened cells located asubstantial distance below the deck section so that the top of saidnonlengthened cell or cells is at a substantial depth below the surfaceof the sea, a drilling structure on said service deck, a bottom deckclosing the bottom of said vertical cells and adapted to be positionedDeep below the sea surface and above the floor of the sea, the wholestructure being constructed and arranged such that the center of gravityof said platform is below the center of buoyancy thereof.
 2. An improvedplatform according to claim 1 further including a drill extending fromsaid service deck down through one of said verticle cells to the seafloor.
 3. An improved platform according to claim 1 wherein said substructure extends at least 70 meters below the surface of the sea.
 4. Animproved platform according to claim 1 wherein said platform includes afirst group of adjacent vertical concrete cells extending from saidservice deck to said bottom deck and a second group of vertical concretecells in surrounding adjacency with said first group and extending fromsaid bottom deck upwards to a point intermediate said service deck andsaid bottom deck.
 5. An improved platform according to claim 1 furtherincluding means for introducing natural deposits into at least one ofsaid vertical cells.
 6. An improved platform according to claim 1further including means for introducing waste materials into at leastone of said vertical cells.
 7. An improved platform according to claim 1wherein at least one of said vertical cells contains solid ballastmaterial.